This invention relates to an improvement in a coin sorting machine in which a bridge circuit is formed with a sorting coil, arranged along a coin passageway, and a standard impedance element, and the balance of the bridge circuit which occurs upon passage of a coin is detected to sort out coins.
A typical one of the conventional coin sorting machine of this type is as shown in FIG. 1.
In FIG. 1, reference characters AB1 through AB4 designate bridge circuits which are formed with a sorting coil Lo whose impedance is varied when a coin inserted into the machine passes therethrough, variable coils L.sub.1 through L.sub.4 adapted as standard impedance elements corresponding to the monetary denominations of coins to be sorted out and variable resistors R.sub.1 through R.sub.4 ; reference character Wo, an oscillation source; reference numerals 1, 11, 12 and 13, differential amplifiers; reference numerals 2, 21, 22 and 23, rectifying and smoothing circuits; reference numerals 3, 31, 32 and 33, comparison circuits; and reference numeral 4, a determination circuit. The number of denominations of coins to be sorted out is four in the coin sorting machine shown in FIG. 1.
When no coin is inserted into the machine, the outputs of the bridge circuits AB1 through AB4 applied to the differential amplifier circuits 1, 11, 12 and 13 are high, unbalance voltages.
When a coin is inserted to pass through the sorting coil Lo, the inductance of the sorting coil Lo is changed and, in response to this inductance change, only the bridge circuit corresponding to the denomination of the coin is balanced. The output of that bridge circuit is subjected to differential amplification in the respective differential amplifier circuit, and is then rectified and smoothed by the respective rectifying and smoothing circuit. The output thus treated is applied to the respective comparison circuit, where it is compared with a reference voltage to detect the balance of the bridge circuit. The output V.sub.1 of the differential amplifier circuit, the output V.sub.2 of the rectifying and smoothing circuit, and the output V.sub.3 of the comparison circuit in this case are indicated by V.sub.1, V.sub.2 and V.sub.3 in FIG. 2, respectively.
The output of the comparison circuit is applied to the determination circuit 4, where it is stored. In the determination circuit, a coin signal (C.sub.1, C.sub.2, C.sub.3 or C.sub.4) corresponding to the denomination of the inserted coin, and a gate signal G for segregating a true coin from a false coin are outputted.
In the above-described machine, at least three (3) amplifiers for differential amplification, rectifying and smoothing, and comparison are required for one denomination; and, accordingly, twelve amplifiers in total are required for sorting out coins of four different denominations. Thus, the conventional coin sorting machine is disadvantageous in that its manufacturing cost is expensive, and the space occupied by the circuit is relatively large. Furthermore, in order to reduce the manufacturing cost as much as possible, it is necessary to eliminate the expensive analog circuits which are disadvantageous in miniaturization.
It is also possible that the input V.sub.2 of the comparison circuit 3 may vary around the reference voltage. In this case, the output V.sub.3 of the comparison circuit is varied. In order to overcome this difficulty, heretofore a voltage hysteresis is given to the comparison circuit as indicated by V.sub.2 in FIG. 2 to achieve, in effect, a two-level comparison. In this case,, however, if the input V.sub.2 of the comparison circuit becomes even slightly lower than the reference voltage, then the sorting signal will be immediately outputted and may be in error.